The present invention relates to a vibrating device having an axially driven movable member, and more particularly to a vibrating device mounted in a portable telephone for signaling a user by vibration of the movable member.
In recent years, there is popularized various portable instruments such as portable telephone, PDA (Personal Digital Assistant), wearable computing instruments and so forth. In these instruments, vibrating devices are mounted for informing signals, by vibration without producing sounds.
FIG. 7 is a perspective view showing a conventional vibration device disclosed in Japanese Patent Laid Open 7-107699. A direct current motor 131 has a rotating shaft 136 supported by a bearing 133. There is formed an annular groove 135 on which an eccentric weight 134 is secured by a fixer 140.
In such a motor, since a commutator and a brush assembly are provided, manufacturing cost increases. It takes a time before the rotating speed approaches 7000˜8000 rpm. Therefore, the device is improper to a device which vibrates in accordance with a music signal. Furthermore, arcs generated between the commutator and brushes cause the quality and the life of the motor to reduce.
The applicant of this patent application has proposed a vibrating device which may remove disadvantages of the prior art.
FIG. 5 is a sectional side view of the vibrating device, FIG. 6 is a sectional view taken along a line VI—VI of FIG. 5.
The vibrating device 210 comprises a cylindrical frame 211 made of a resin, a vibrating assembly 220 axially movably mounted in the frame 211, and a magnetic driving device 219 mounted in the frame 211 at an end thereof.
The vibrating assembly 220 comprises a cup-shaped yoke 221 having a bottom 221b, a cylindrical permanent magnet 222 secured to the yoke 221 at the axis thereof, and a pair of weights 223a and 223b secured to the outside and inside of the bottom 221b of the yoke 221. The yoke 221 is slidably supported by three projections 214 formed on the inside wall of the frame 211, so that the vibrating assembly 220 can be smoothly vibrated.
The vibrating assembly 220 is resiliently held at a neutral position by a pair of coil springs 224 and 225 provided between both axial ends and the frame 211.
The magnetic driving device 219 comprises a coil bobbin 213 cantilevered in the end of the frame 211 and a driving coil 212 provided on the coil bobbin 213. The coil bobbin 213 is made of a metal pipe, on the peripheral surface of which is formed an insulation layer. The coil bobbin 213 is inserted in a space 226 between the yoke 221 and the permanent magnet 222.
The primary resonance frequency of the vibrating assembly 220 is 100–160 Hz, the vibration at which is properly transmitted to the user's body. An alternating signal having a basic frequency of the primary resonance frequency is applied to the driving coil 212 from terminals 235 and 236, so that the vibrating assembly 220 is axially vibrated.
However, large friction generates between the outside wall of the vibrating assembly 220 and the inside wall of the frame 211, because of a large sliding area there-between. The large friction causes the efficiency of the device to reduce.